Burner assembly for lean fuel gases



Feb. 13, 1968 R. D. REED BURNER ASSEMBLY FOR LEAN FUEL GASES Filed Feb.5, 1966 l/vvE/vrak ROBERT D. REED" 19 ATTORNEY United States Patent3,368,605 BURNER ASSEMBLY FOR LEAN FUEL GASES Robert D. Reed, Tulsa,Okla., assignor to John Zink Company, Tulsa, Okla, a corporation ofDelaware Filed Feb. 3, 1966, Ser. No. 524,727 2 Claims. (Cl. 1587) Thepresent invention relates to apparatus for the combustion of gaseousmaterials and the invention more specifically pertains to a burnerassembly wherein gases of low heat value are burned under aself-sustaining combustion conditions so that the heat developed fromthe burning of the combustible components in waste gases may berecovered for useful purposes.

In the chemical and process industries gases are produced and many carrycombustible components. The combustibles present in such gaseousproducts are usually in the low mol-percentage range and often containless than two hundred British thermal units for each cubic foot of gas.Such low heat content gases are difiicult to burn under self-sustainingcombustion conditions. Equipment for treating such gaseous products andauxiliary apparatus in association with the burner have been employed inthe past to burn such gases but because of the costs of such equipmentand apparatus such gases have often been disposed to waste which alsoinvolves considerable expense.

It is accordingly an object of the present invention to provideapparatus for the combustion of lean fuel gases without the necessity ofproviding equipment for pretreatment of such gaseous products andwithout the necessity of employing complicated apparatus in order toprovide for stable combustion of the diluted fuel gases.

A more specific object of the invention is to provide apparatus for thecombustion of fuel gases of low heat content wherein air for mixing withthe fuel gases is caused to move circumferentially as the fuel isdelivered into the whirling air to thereby maintain the fuel mixturewithin the burning zone for a protracted period and to provide means forpreventing the rapid transfer of heat from the combustion zone therebymaintaining a high temperature within the burner assembly wherein thecombustion reactions can proceed at a high rate and thereby insureself-sustaining combustion of a lean gaseous fuel.

Another object of the invention is to provide structure within theburner assembly insuring thorough mixing of adequate quanities of airwith the fuel gas to provide a stoichiometric mixture of the fuel gasand air within the heat shielded portion of the assembly to provide forburning time and temperature levels within the combustion zone whichinsure stable burning of lean fuel gases.

Other objects and features of the invention will be appreciated andbecome apparent to those skilled in the art to which the inventionpertains as the present disclosure proceeds and upon consideration ofthe following detailed description taken in conjunction with theaccompanying drawing wherein apparatus embodying the invention isdisclosed.

In the drawing:

FIG. 1 is a sectional view taken along the axis of a burner assemblyexhibiting the invention.

FIG. 2 is a fragmentary sectional view taken on the line 22 of FIG. 1.

FIG. 3 is a fragmentary development view of the vane assembly takengenerally on the line 3-3 of FIG. 2.

A burner assembly embodying the invention is shown a ICC.

in the drawing in operative relationship with a Scotch- Marine Boilerwherein heat rapidly transfers from the combustion zone to a corrugatedfire tube and to the water therein. It will be appreciated that theburner assembly may be employed for other purposes and for heating anytype of structure or for firing into a furnace chamber. The burnerassembly includes an annular shaped ceramic member 10 with an endportion extending into the water tube 12 with the outer surface disposedalong the corrugated wall 11. The ceramic member 10 has a centralopening and the downstream end of the cylindrical wall surface 14 isdefined by the annular shoulder 16 which has a face arranged in a planeat right angles to the axis of the burner assembly and the axis ofthecentral opening in the ceramic member 10. A larger diameter opening isprovided in the downstream end portion of the ceramic member 10 toprovide a cylindrical wall surface 18 spaced inwardly from thecorrugated wall 11 of the water tube 12.

A housing 21 surrounds the upstream portion of the ceramic member 10 andmay be secured to the boiler tube structure by means of a flange 22 andbolts 23. The upstream end of the cylindrical housing 21 is closed bymeans of an end wall 24 and a detachable disc-shaped element 26 as shownin FIG. 1. An annular wall 27 is mounted within the housing 21 andarranged coaxially therein. A ring shaped plate 28 covers the upstreamend of the ceramic member 10 and it may be joined to the cylindricalhousing 21 and to the annular wall 27 in any suitable manner such as bywelding. The cylindrical wall 27 may likewise be welded to the end wall24 to provide an annular chamber 31 within the housing'Zl.

An inlet opening 32 is provided in the perimeter of the housing 21 and aduct 33 extends radially outward therefrom whereby air under pressuregreater than atmospheric may be delivered into the chamber 31. Theincoming air moves in a direction which is radially of the annular wall27 which acts as a baflle to distribute the air in the direction of thearrows 34 and 36 in FIG. 2. The annular wall 27 is proviled with twoopenings 37 and 38 which are arranged diametrically of each other asbest shown in FIG. 2. The openings 37 and 38 are circumferentiallydisplaced from the inlet opening by approximately ninety degrees. Thevelocity of the air entering through the inlet opening 32 is virtuallydissipated by impact with the wall 27 and a supply of air is stored inthe chamber 31.

A tubular member 41 extends through an opening in the disc-shapedelement 26 and is disposed substantially concentrically with the annularwall 27. The downstream end of the tubular member 41 terminates withinthe central opening in the ceramic member 10'. An annular chamber 45 isprovided between the annular wall 27 and the tubular member 41. A leanfuel gas is admitted into the tubular member 41 through a conduit fitting 42. A guide tube 44 extends along the axis of the tubular member 41and carries a frusto-conical element 46 at the end thereof spaced fromthe downstream end of the tubular member 41. The fuel gas is thusdeflected in generally radially outward directions by impingement withthe concave face of the generally frusto-conical shaped element 46. Theguide tube 44 may be supported at the downstream end in any suitablemanner (not shown).

The burner assembly includes means which insures mixing of air with thefuel gas and also functions to retain the mixture within the ceramicmember for a protracted period to develop a high temperature combustionzone. Such means takes the form of a vane unit 48. This unit issupported on the tubular member 41 by a ring member which is L-shaped insection and which is attached to the downstream end of the tubularmember 41. A flange 49 of the ring member carries a plurality of vanes51 which radiate therefrom. The vanes 51 are of such lengths measuredradially thereof that the outer ends fit within the central opening inthe ceramic member 10 and are in abutting relationship with thecylindrical wall surface 14. The vane unit also supports the inner endof the tubular member 41 to maintain it substantially concentric withthe axis of the burner assembly.

Each of the vanes 51 is arranged in one plane as best shown in FIG. 3and all of the vanes are inclined in the same direction in proceeding inone direction circnmferentially of the assembly. The vanes 51 are soconstructed and arranged that the downstream edge portion of one vane 51overlaps the upstream edge portion of an adjacent vane and this overlaparea 53 is indicated by dotted lines in FIG. 3. Thus air moving from thechamber 45 is forced to move by the vanes 51 circumferentially withinthe central opening in the ceramic member 10. The overlapping of thedownstream edge portion of one vane with the upstream edge portion ofanother vane insures that there will be no axial movement of the air asit passes through the vane unit 48.

The radial web of the ring member which supports the vanes 51 isprovided with a plurality of circumferentially spaced relatively smallports 56 as shown in FIGS. 1 and 2 through which minor quantities of airmay move from the chamber 45 into the ring member. The tubular member 41is also provided with a plurality of relatively small circumferentiallyspaced ports 57 (FIG. 1) through which small quantities of the fuel gasmay escape to a position within the ring member. The air escapingthrough the ports 56 is mixed with the gas escaping through the ports 57and this mixture is shielded from the lean fuel gas moving in spacebetween the guide tube 44 and the tubular member 41 and the air-gasmixture within the ring member is shielded from the air passing over thevanes 51. There is slow burning of the mixture within the ring memberand this assists in starting the burner particularly when the structureis cold.

In operation air under pressure is supplied into the chamber 31 throughthe inlet duct 33. The entering air impinges against the annular wall 27and is accommodated in the chamber 31 virtually free of velocity. Theair passes into the chamber 45 through the openings 37 and 38. Thepressure within the chamber 45 is less than that in the chamber 31. Thepressure in the chamber 45 is greater than the pressure Within thecombustible zone or the area 58. There is a drop in pressure as the airmoves through the vane unit 48. A circumferential component is impartedto the air as its velocity increases in passing between the vanes 51 sothat the air moves circumferentially along the cylindrical surface 14 asa whirling air mass. The lean fuel gas supplied through the inletconduit 42 moves axially within the tubular member 41 and is divertedgenerally radially outward into the whirling air. A pronounced pressuredrop results from the air moving over the vane unit 48 and creates a lowpressure condition for the air in the area represented at 61 in FIG. 1which tends to draw the fuel gas thereinto whereby fuel gas is mixedwith the air. Combustion is initiated and the burning of the fuel takesplace in an annular area represented at 62 in FIG. 1.

The pressure drop as a consequence of the air fiowing through the vanes51 develops a pressure in the area 61 which is lower than atmosphericand lower than the pressure in the area 58. The low pressure in the area61 develops a low pressure zone at 63 which is less than the pressure inthe area at 58 but greater than the pressure in an annular area 64adjacent the cylindrical wall surface 18. These pressure zones and thecontour of the ceramic member 10 induce the return of hot gases asrepresented at the arrows 66 into the central portion of the combustionzone. Thus the forward or downstream movement of the burning gas ischecked and held close to the burner head and in the zone where the gasescapes from the tubular member 41.

The burning accordingly takes place principally in the annular area 62which is shielded by the ceramic member 10. The insulating character ofthe ceramic member prevents rapid loss of heat to the fire tube 12. Thusthe temperature is maintained at a high level within the ceramic member10 and the combustion reactions proceed at a high rate as a consequenceof the high temperature to promote self-sustaining combustion and stableburning of a lean fuel gas. The hot gases as indicated by the dottedarrows 66 return to the central portion of the combustion zone toprovide added heat for maintaining of the temperature of both the airand the gas to the auto-ignition temperature of the fuel mixture. Theshoulder 16 serves to develop eddies of the burning fuel as indicated bythe arrows to further maintain a high temperature in the combustionzone.

An auxiliary fuel burning device may be provided for insuring stableburning if the heat content of the fuel gas is inadequate for a requiredquantity of heat. A burner nozzle 63 may be introduced through the guidetube 44 and arranged within the frusto-conical element 46 fordischarging fuel of a high heat value within the combustion zone.

While the invention has been described with reference to a fuel burnerassembly in association with one type of boiler to be heated it will beappreciated that the burner assembly has utility for other heatingpurposes. Various modifications may be made in the elements of theassembly as well as changes in the overall organization. Suchmodifications and others may be made without departing from the spiritand scope of the invention as set forth in the appended claims.

What I claim and desire to secure by Letters Patent 1. In apparatus forthe combustion of lean fuel gases, a ceramic member having a centralopening therein defined by a substantially cylindrical surface, saidceramic member having a second opening at the downstream end thereofdefined by a substantially cylindrical surface of larger diameter thansaid central opening, an annular shoulder on the ceramic member disposedin a plane substantially at a right angle to the axis of said centralopening and defining the downstream end thereof and defining theupstream end of the second opening, a tubular member extending into theupstream portion of the central opening for guiding fuel gas thereinto,means for diverting the fuel gas generally radially outwardly from saidtubular member adjacent the upstream portion of said central opening,means providing an annular chamber around said tubular member, means forguiding air into said chamber, a vane unit disposed around said tubularmember within the upstream portion of said central opening, said vaneunit having vanes which slope in the same manner in proceeding in onedirection circumferentially of the ceramic member, the downstream edgeportion of each vane overlapping the upstream edge portion of anadjacent vane whereby substantially all of the air from said chamber inmoving through said vanes is deflected circumferentiaily within thecentral opening and in the presence of the diverted fuel gas, and meansreleasing minor quantities of air from said chamber and minor quantitiesof fuel gas from within said tubular member at locations radiallyinwardly of said vane unit for axial downstream movement around saidfuel diverting means.

2. In apparatus for the combustion of lean fuel gases according to claim1 wherein the outer ends of said vanes are in abutting relationship withthe cylindrical surface of the central opening.

References Cited UNITED STATES PATENTS 2,855,033 10/1958 Furczyk 1587 X6 2,976,919 3/1961 San-born 158-1.5 X 3,195,609 '7/1965 Nesbitt et a1.158-15 X FOREIGN PATENTS 303,030 1/ 1955 Switzerland.

FREDERICK L. MATTESON, IR., Primary Examiner. E. G. FAVORS, AssistantExaminer.

1. IN APPARATUS FOR THE COMBINATION OF LEAN FUEL GASES, A CERAMIC MEMBERHAVING A CENTRAL OPENING THEREIN DEFINED BY A SUBSTANTIALLY CYLINDRICALSURFACE, SAID CERAMIC MEMBER HAVING A SECOND OPENING AT THE DOWNSTREAMEND THEREOF DEFINED BY A SUBSTANTIALLY CYLINDRICAL SURFACE OF LARGERDIAMETER THAN SAID CENTRAL OPENING, AN ANNULAR SHOULDER ON THE CERAMICMEMBER DISPOSED IN A PLANE SUBSTANTIALLY AT A RIGHT ANGLE TO THE AXIS OFSAID CENTRAL OPENING AND DEFINING THE DOWNSTREAM END THEREOF ANDDEFINING THE UPSTREAM END OF THE SECOND OPENING, A TUBULAR MEMBEREXTENDING INTO THE UPSTREAM PORTION OF THE CENTRAL OPENING FOR GUIDINGFUEL GAS THEREINTO, MEANS FOR DIVERTING THE FUEL GAS GENERALLY RADIALLYOUTWARDLY FROM SAID TUBULAR MEMBER ADJACENT THE UPSTREAM PORTION OF SAIDCENTRAL OPENING, MEANS PROVIDING AN ANNULAR CHAMBER AROUND SAID TUBULARMEMBER, MEANS FOR GUIDING AIR INTO SAID CHAMBER, A VANE UNIT DISPOSEDAROUND SAID TUBULAR MEMBER WITHIN THE UPSTREAM PORTION OF SAID CENTRALOPENING, SAID VANE UNIT HAVING VANES WHICH SLOPE IN THE SAME MANNER INPROCEEDING IN ONE DIRECTION CIRCUMFERENTIALLY OF THE CERAMIC MEMBER, THEDOWNSTREAM EDGE PORTION OF EACH VANE OVERLAPPING THE UPSTREAM EDGEPORTION OF AN ADJACENT VANE WHEREBY SUBSTANTIALLY ALL OF THE AIR FROMSAID CHAMBER IN MOVING THROUGH SAID VANES IS DEFLECTED CIRCUMFERENTIALLYWITHIN THE CENTRAL OPENING AND IN THE PRESENCE OF THE DIVERTED FUEL GAS,AND MEANS RELEASING MINOR QUANTITIES OF AIR FROM SAID CHAMBER AND MINORQUANTITIES OF FUEL GAS FROM WITHIN SAID TUBULAR MEMBER AT LOCATIONSRADIALLY INWARDLY OF SAID VANE UNIT FOR AXIAL DOWNSTREAM MOVEMENT AROUNDSAID FUEL DIVERTING MEANS.